1. Field of the Invention
The invention relates to a torque limiter device capable of transferring torque from a power source to a driven device, and further capable of disengaging the torque transfer connection when an overload is encountered.
2. Description of the Related Art
A torque limiter device has been put forth in Japanese unexamined patent publication No. 53-67407 (Int.Cl.F16D 7/06) and Japanese unexamined utility model publication No. 4-68228 (Int.Cl.F16D 43.20). This type of torque limiter is comprised of a torque input part connected to a torque generating power source, and a torque output part rotatably installed opposite to the aforesaid torque input part on the same shaft. A roller-type torque transmission device is installed between the aforesaid torque input and torque output parts in a manner as to allow the torque from the input side to be transferred to the output side without any power loss during normal operation. In the event that an excessive load is generated, the aforesaid torque transmission part operates so as to mechanically disengage the joint between the aforesaid torque output and torque input parts.
The aforesaid rollers are rotatably attached to the torque input part within receiver orifices formed therein, and form a connection with the torque output part by means of their partial insertion within concavities disposed opposite to the aforesaid torque input part. The rollers are preloaded at a specific pressure as means of maintaining their positions within the aforesaid concavities during normal torque transfer operation. This structure consists of the aforesaid torque input part, torque transmission part, and torque output part, and operates as a single rotating assembly at the time when the aforesaid rollers are residing in the aforesaid concavities. However, an excessive load generated from the torque limiter's output side will overcome the preload applied to the rollers with the result that the rollers are forced out of the concavities. This action disengages the mechanical connection between the input and torque output parts, allows said parts to rotate independently, and thus interrupts the transmission of torque from the input to the output side.
In this type of torque limiter, bearings are utilized as means of providing rotational support for the torque input and output parts. Multiple bearings, in the form of separate thrust and radial bearing units, have been conventionally required as means of maintaining the torque input and output parts in precise orientation during their rotation.
The torque limiter presented by the aforesaid Japanese unexamined patent publication No. 53-67407 prescribes the use of needle and ball bearings to support loads on the thrust axis, and needle bearings on the radial axis. The torque limiter presented by the aforesaid Japanese unexamined utility model publication No. 4-68228 prescribes a pair of ball bearing structures installed over a flange formed on the inner periphery of the aforesaid torque output part, said bearings having the purpose of receiving both radial and axial thrust loads applied through the aforesaid flange.
The torque limiter prescribed by the aforesaid publication No. 53-67407 utilizes three separate bearings, and that prescribed by the aforesaid publication No. 4-68288 utilizes two bearings. Both of these patents prescribe torque limiter structures in which radial and thrust loads are received by correspondingly separate bearing units, thus necessitating that space be provided for these multiple bearings.
Moreover, the preload, which is applied to the rollers installed between the torque input and torque output parts, operates against the torque output part, thus necessitating that the bearing at the torque output part not only be strong enough to support operating loads, but be further capable of withstanding roller preload. This design results in a relatively complex bearing structure which necessitates that the torque limiter be fabricated to dimensions that are often larger than preferred. Furthermore, applying roller preload against the torque output part necessitates that the torque output part be made to a relatively thick dimension. Considering that the torque input part is solidly fixed to the shaft emanating from the torque generating power source, and that it offers an inherently high degree of strength and sufficient thickness, it would thus seem preferable to preload the rollers against the torque input part only.
As can be inferred from the above discussion, the use of multiple bearing units, the need for high-strength bearings, and the necessity of fabricating the torque output part to sufficient thickness to withstand roller preload can be construed as structural shortcomings that result in a torque limiter requiring fabrication to external dimensions which are often larger than desired.